When the luxation of both bones backwards is simple, and by mistake or neglect has been left unreduced, the case soon becomes irreme diable; the patient for ever loses the power of fully flexing the fore-arm, and the muscles of the arm become more or less atrophied ; the powers of pronation and supination also become impaired, but extension of the elbow-joint can be performed.
Sir A. Cooper had an opportunity of dissect ing a compound luxation of the elbow-joint, in which the radius and ulna were thrown back wards, and the specimen is preserved in the Museum of St. Thomas's IIospital, and a re presentation given in his work on dislocations: see plate xxiii. fig. 2. The coronoid process of the ulna was thrown into the posterior fossa of the os humeri, and the olecmnon projected at the back part of the elbow, above its natural situation, an inch and a balf. The radius was placed bebind the external condyle of the os humeri, and the humerus was thrown forwards on the anterior part of the fore-arm, where it formed a large projection. The capsular liga ment was torn through anteriorly to a great ex tent ; the coronary ligament remained entire. The biceps muscle was slightly put on the stretch by the radius receding, but the brachia lis anticus was excessively stretched by the altered position of the coronoid process of the ulna.
This was a recent case ; but it would ap pear from the dissections which have been made of cases which had been left for a long time unreduced, that a new bony cavity had been made on the front of the coronoid process of the ulna, while the brachialis anticus be came the seat of ossific depositions. An in teresting case of this kind is recorded by Cru veilhier, and figured by him in his Anat. Pathol. plate iv. fig. 1. Nclard also met with a simi lar case in dissection.
2. Lateral dislocation of the bones of the fore arm.—Lateral dislocations of the elbow-joint are rare, and this circumstance is owing to the great transverse extent of the articular surfaces, to the inequalities which the corresponding surface of the humerus presents in the transverse di rection, to the strength of the lateral liga ments, and the attachment to them of the tendons of those superficial muscles which pass to the anterior and posterior part of the fore-arm, which tendons almost identify themselves with the lateral ligaments, and must considerably strengthen and support the joint laterally.
Again, the force which would have a tendency to luxate the bones laterally can very rarely be directed in such a manner as to produce the luxation we are now considering, nor are the muscles ever so directed as to produce them.
We find in authors circumstantial accounts of the symptoms of the complete luxation outwards and also of the complete luxation inwards ; but we have not had any opportuni ties ourselves of witnessing these complete luxa tions as the immediate result of accidents. Indeed we can scarcely conceive any complete luxation outwards to correspond exactly to the description given ; as we imagine that when ever the bones of the fore-arm are completely thrown outwards, these bones must be drawn - immediately upward along the outer side of the arm. We can conceive it possible, however, that the bones of the fore-arm may be completely dislocated inwards from the trochlea of the humerus, and still be restrained from yielding to those forces which would draw them upwards and inwards, by the great pro jection inwards of the internal condyle of the humerus, which we know is so much more prominent than the external. We could scarcely mistake the case of complete lateral luxation of the fore-arm, whether it was inwards or outwards.
In the incomplete lateral luxations of the bones of the fore-arm at the elbow-joint, the articular surfaces of the bones are still in con nexion, but the points of contact of their naturally corresponding surfaces are altered more or less as to their relative positions to each other. In these luxations the bones of the fore-arm may be thrown partially outwards or partially inwards. In the luxation outwards, the cavity of the superior extremity of the radius abandons the lesser head of the humerus, and its cup-like extremity may be felt beneath the skin, while the great sigmoid cavity of the ulna corresponds to the capitulum of the humerus from which the radius has been dis placed. As to the anatomy of the parts under such circumstances, the ligaments must be all torn, the biceps and triceps muscles must be pulled outwards in the direction of the bones of the fore-arm, into which they are inserted, the supinator brevis muscle cannot escape lace ration, and the musculo-spiral nerve must be more or less stretched. There must be danger of such a luxation being rendered complete or even compound.